From ATI Web Site What is a differential drive amplifier?
A truly differential drive amplifier, consists of two complete amplifiers for each channel: one + amplifier and - amplifier. The positive input signal is amplified by the positive amplifier and the negative input signal is amplified by the negative amplifier when a balanced signal is applied to the input. There is no ground reference since the output signal is derived from the combination of the positive signal and the negative signal. A differential drive amplifier is sensitive to the difference between the positive and negative input signals resulting in those signals common to the input being cancelled. The input stages of each channel of the amplifier are of differential design all on one substrate resulting in the reduction of hum and turn-on/turn-off pops. This is referred to as "common mode rejection".
ATI
